The 3G standards group is currently considering various proposals for the long term evolution (LTE) of the 3G RAN. The LTE has been driven by the needs for reducing cost, improving spectral efficiency, facilitating support for revenue increasing services, improving operation and maintenance (O&M) and service provisioning, increasing throughput, reducing end-to-end delay during call setup, having seamless mobility, or the like.
FIG. 1 illustrates conventional 3G network 100. The conventional 3G network 100 includes an RAN 110, (comprising a plurality of Node-Bs 112 and a radio network controller (RNC) 114), and a core network (CN) 120. The CN 120 includes a packet switched domain 122 and a circuit switched domain 132. The packet switched domain 122 includes a serving GPRS support node (SGSN) 124 and a gateway GPRS support node (GGSN) 126. The circuit switched domain 132 includes a mobile switching center (MSC) 134 and a gateway MSC (GMSC) 136. The CN 120 also includes an IP multimedia subsystem (IMS) 128.
The 3G standards currently specify that layer 2 (i.e., medium access control (MAC) layer) functionalities be split between the Node-B 112 and the RNC 114. The Node-B 112 performs radio resource management (RRM) for implementing high speed downlink packet access (HSDPA) and high speed uplink packet access (HSUPA). Layer 3 functionality (i.e., radio resource control (RRC)) resides in the RNC 114. It has been proposed that to reduce end-user latency, user and control plane separation in the RAN 110 should be implemented so that optimized routing of user-plane and control-plane data may be achieved. Furthermore, many RRC functionalities currently implemented by the RNC 114 may be moved to the Node-B 112 for enabling faster communication. This would remove multiple signaling and should help in reducing latency. It has also been proposed that latency in the RAN 110 is not affected by moving the RRC functionalities into the Node-B 112 (or alternatively removing the RNC 114 completely).
FIG. 2 is a signaling diagram of a conventional call setup procedure 200. The RAN 110 broadcasts system information via a broadcast channel (BCH) (step 202). A wireless transmit/receive unit (WTRU) 101 receives the system information while the WTRU 101 is in an idle state. The call setup is performed by the steps of establishing an RRC connection, establishing an RRC signaling connection and establishing a radio bearer. The RRC layer of the WTRU 101 leaves an idle state and sends an RRC connection request to the RAN to establish the RRC connection (step 204). Upon reception of the RRC connection request, the RRC layer of the RAN 110 selects radio resource parameters and sends an RRC connection setup message including the radio resource parameters to the WTRU 101 (step 206). Upon reception of the RRC connection setup message, the RRC layer of the WTRU 101 configures physical and MAC layers based on the radio resource parameters to establish the RRC connection. Upon establishment of a local radio link control (RLC) signaling link, the WTRU 101 sends an RRC connection complete message to the RAN 110 (step 208).
In order to establish an RRC signaling connection, a non-access stratum (NAS) of the WTRU 101 sends an initial direct transfer message to the RRC layer of the RAN 110 (step 210). The initial direct transfer may be a connection management (CM) service request (step 212), which is acknowledged by a CM service accept message (step 214).
In order to establish a radio bearer, the RRC layer of the RAN 110 sends a radio bearer setup message to the RRC layer of the WTRU 101 (step 216). The radio bearer setup message includes physical layer, MAC layer and RLC layer parameters. After receiving the radio bearer setup message, the WTRU 101 configures physical layer and MAC layers, and sends a radio bearer setup complete message to the RRC layer of the RAN 110 (step 218).
One of the problems of the conventional call setup procedure is a multi-layer call setup procedure that occurs in the RAN 110. This is primarily due to legacy complications as well as the separation imposed between the MAC and the RRC layers, with the MAC layer in the Node-B 112 and the RRC layer in the RNC 114. Therefore, it would be desirable to provide a simplified call setup procedure in the RAN 110.